The present invention relates to a device for recognizing the impact site of a charge carrier beam.
Devices of this type are used in particular with electron beam vaporizer sources, melting installations, and welding guns. In the case of all of these installations it is important to guide the electron beam precisely. So for example in the electron beam vaporizer sources the electron beam is moved over the surface of the material to evaporate in such manner that on a given area the most uniformly possible surface temperature is achieved and hence an evaporation rate which is constant over this area. To make possible precise guidance of the electron beam which can be deflected through electrical and/or magnetic fields, it is required that the actual position is precisely known.
For the determination of the actual position different properties are utilized which the impact site of the electron beam on a material has. One of these characteristics consists in that the target material at the impact site melts while it is still solid in other places. Other characteristics are the increased emission of UV light at the impact site and the emission of X-rays which are generated in the deceleration of electrical particles.
For the monitoring of the beam impact area in particle beam working equipment an arrangement is already known which has a control beam path for a bundle of the particle and/or X-ray beams emitted by the beam impact area, wherein the control beam path has an imaging system for imaging the beam impact area as well as an radiation receiver arranged in the image area of the imaging system (DE-AS 12 99 498). However, with this known arrangement it is not possible to obtain a precise coordinate specification of the impact site of the electron beam on a target because the effective area of the radiation receiver is smaller than the area of the image of the beam impact area generated by the imaging system at optimum focussing of the working particle beam, i.e. the entire radiation receiver is covered by the imaged beam impact area.
A device for recognizing the impact site of a charge carrier beam on a target, in which the impact area of the electron beam imaged on a sensor by an imaging system is smaller than the sensor, is also known (EP-0 184 680 Al). Herein an imaging system is provided which detects all positions which the impact site can assume and images them on the sensor surface of a position-sensitive detector. It is of disadvantage in this known device that the actual position signal is falsified by potentially occurring level changes of the melt material, i.e. the determined x,y-coordinates of the impact site are influenced by changing the z-coordinate. In large sputtering installations which represent the preferred application field of this known position sensor, the shortest distance of the detector and the diaphragm from the target surface is generally great in relation to the maximum height change of the melt material surface so that the deviation of the indicated from the actual x,y-coordinates brought about by this level change is negligibly small.
In smaller sputtering installations electron beams of lower power are generally used. Therefrom results a significantly lesser intensity of the X-radiation which can be utilized for the position detection. In such installations the position detectors must therefore be disposed at a significantly shorter distance from the target surface. Also, the distance between the target surface and the positioning detector is necessarily small due to construction limitations. But therewith due to the other imaging scale a change of the z-coordinate of the beam impact point--even at constant x,y-coordinates--effects a shift of the picture point on the detector surface which is no longer negligible. The position detector according to EP-0 184 680 Al is therefore less suitable for small installations in which the melt bath level is variable.
Level changes as such could be detected with the aid of distance measuring devices such as are used for example in a modern autofocus camera. Such distance measuring devices however permit no detection of the x-and y-coordinates.